Switching mechanism



March 9, .1943. H. EQMALONE SWITCHING MECHANISM 7 Filed 001;. "so, .1940 ZISheetS-Sheec r1 a7 6/ 70 29- I a INVENTOR.

F y-:5 BY Harmer El -[alums I I W ATTORNEY.

March 9, 1943. ON 2,313,083

SWITCHING- MECHANISM Filed Oct. 50, 1940 2 Sheets-Sheet? INVENTOR. f HumErE EZUZZE 2/" I a I ATTORNEY. Q

Patented Mar. 9, 1943 2,313,083 SWITCHING MECHANISM Homer E. Malone, Milwaukee, Wis., assignor to Perfex Corporation, Milwaukee, WlS., a corporation of Wisconsin Application October 30, 1940, Serial No. 363,431

14 Claims.

This invention relates generally to switching mechanisms, and more particularly to the type of device wherein the switching mechanism is actuated by a condition responsive means to control an electric circuit.

The invention has particular utility in connection with the automatic control of a burner for a heating plant for example, where it is desirable that some provision be made for quickly stopping the operation of the burner in the event of combustion or ignition failure, in order that hazardous conditions may be obviated.

It is an object of the invention to provide an improved connection between a thermally responsive member and a circuit controlling mechanism whereby upon motion of the thermally responsive member in response to changes or reversals in temperature affecting the same, the controlling mechanism is operated immediately, and upon continued motion of the thermally responsive member no further motion is imparted to the controlling mechanism.

An object of the invention is to provide an improved slip friction connecting means between a temperature responsive device and the switch elements which is simple and compact in construction, reliable in operation, which is adaptable for operation with various types of temperature responsive devices, and which will pro-- duce the desired sequence of operations.

A further object is to devise an improved slip friction switching mechanism which is adaptable for operation with temperature responsive element located at a point remote from the switching mechanism.

A still further object is to provide a slip friction mechanism in which the constituted elements thereof are arranged in a common plane for movement in a linear direction by the thermal device whereby stresses or bending of any of the elements is eliminated and correct operation is insured.

Another object is to provide an improved slip friction mechanism in which the associated elements are always maintained under a state of tension in order that no lost motion may impede the instantaneous reliable operation of the device.

It is a further object to devise an improved slip friction mechanism in which the operating mechanism and the contact elements are all arranged upon a single supporting member or plate so that the assembly, adjustment and accessibility of the elements are facilitated.

A further object is the provision of an improved flame detecting switching mechanism in which a plate-like element is arranged to buckle upon the presence of flame, this member being biased in this buckling direction by the switching mechanism.

Other objects and advantages of the improved slip friction switching device reside in certain novel features of construction, arrangement and combination of the various elements which will be hereinafter more fully described, particularly pointed out in the appended claims, and illustrated in the accompanying drawings in which:

Fig. 1 shows a cross-sectional side elevation of the switching mechanism and the associated thermally responsve device both mounted upon a burner apparatus;

Fig. 2 is a top view of the switching mechanism;

Fig. 3 is an end cross sectional view taken along the line 3--3 of Fig. 1;

Fig. 4 is a similar view taken along the line 4-4 of Fig. 1;

Fig. 5 is a fragmentary view of a gun type of burner installation on a furnace to which the invention is applied;

Fig. 6 is a top view of a modified form of the switching mechanism;

Fig. '7 is a cross sectional end view taken along the line 'l--'l of Fig. 6;

Fig. 8 is a cross sectional side view of the modified form of the invention;

Fig. 9 is a bottom view of the mechanism;

Fig. 10 is a fragmentary view of a burner installation to which the modified form of the switching mechanism is applied; while,

Fig. 11 is an end view of the burner illustrating a form of thermal responsive device applicable to the modified switching mechanism.

The invention comprises generally the combination of a thermal responsive device indicated at 5 and a control device or switching mechanism associated therewith indicated at 6, both elements being arranged for example upon a burner installation as indicated in Fig. 5. The thermal responsive device 5 is arranged within an enclosing chamber or casing preferably in the form of a casting 1, having fairly thick walls including a flat bottom wall 8 through which a bolt 9 passes and is threaded into the side wall 10 of the blast tube-of a burner for supporting the casting l. A pair of downwardly projecting legs, one of which is shown at H, straddle the tube l0 and serve to space the bottom wall 8 from direct thermal contact with the tube I0. The casing I has semi-circular side and top walls and is provided with an opening l2 in the front thereof. The upper portion of the wall extending toward the opening 52 is gradually sloped downward as indicated at 3. The opening [2 is arranged so as to face the combustion chamber of a furnace as shown in Fig. 5. The rear or opposite end of the casing 7 is arranged with a cylindrical wall [4 having a shoulder portion formed therein to provide a seat for a flat metal disc l5 which closes off the end of the casing l and lowers the transmission of heat through the casing 7 to the switching mechanism 6. This disc [5 also prevents the escape of the combustion gases through the thermal unit and prevents any drafts of air caused by the chimney drafts in the furnace from entering the thermal unit 5 and affecting the reliable operation of the unit.

The thermal responsive device 5 is supported within the casing "I by means of a supporting tube it passing through an opening in the disc 15. An operating rod or shaft ii passes axially through the tube i5 and projects outwardly from the front end thereof. The condition responsive or thermal operated device includes a relatively thin flat annular disc member or diaphragm 58 having a rearwardly projecting flange portion i9 formed thereon which engages the periphery of a second relatively fiat annular disc member 29. The disc 29 is supported upon the end of tube it: as shown at 2!. The disc i8 is ar ranged at its front surface to receive and absorb radiant heat waves or energy emanating from the burner flame. These radiant heat waves pass through the openin' i2 and impinge upon the front surface of the diaphragm E8. The diaphragm i8 is preferably constructed of a material having a relatively high thermal coemcient or" expansion. It is bowed outward toward the opening 52 a slight amount as a result of a shoulder on the shaft 1? engaging the same and applying a slight amount of pressure to the diaphragm. The shaft i? as will be hereinafter pointed out is normally spring urged in adirection toward the diaphragm is. The second disc 2 arranged upon the peripheral rear edge I9 of the diaphragm is is preferably made of a material having a somewhat smaller coefficient of heat expansion than the material of which the diaphragm i8 is constructed. The disc is thicker than the diaphragm and preferably spot welded at recurring intervals to the periphery id of the diaphragm. The diaphragm iii upon being subjected to elevated temperatures such as caused by radiant heat waves bows or bulges outward while the annular disc 26 expands circumierentially at a somewhat slower rate than the diaphragm. The end of the shaft i? loosely projects through a hole in the center of the diaphragm so as to guide and support the end of the shaft.

The control device of the invention which is actuated by the operation of the thermal responsive device 5 is shown in the form of a switch actuating mechanism (3. This switching mechanism is suitably enclosed in a rectangular shaped metal casing or housing which is supported by means of an angular U-shaped bracket 27 and screw 23 upon the top of the blast tube iii of the burner. The bracket 27 comprises a pair of legs, one of which is shown, which straddle the tube ii and have their lower ends bent to conform to the cylindrical shape of the tube and are secured thereto by screws 2- This screw 29 passes through a slot 39 of each bracket leg 2? so that the bracket and the switching mechanism 6 may be adjust-ably positioned longitudinally within certain limits along the surface of the blast tube H3. By means of this adjustment the element supporting tube i6 and the thermal device 5 may be laterally positioned within the casing i at any desired location either closer or further away from the opening 82 of the casing 6, depending upon the intensity of the burner flame within the combustion chamber so that the correct response of the thermal element may be more accurately and reliably gauged. In the case of a very hot fire the thermal device 5 would be positioned further away from the opening l2, whereas in the type of burner in which a lower flame would exist the thermal device 5 would be adjusted closer to the opening i2.

A sheet metal enclosing cover 3i is provided for protecting the switching mechanism 6. It is adjustably attached to the blast tube ill by means of a screw on each side riding in a slot 33 so that the cover 3i may be shifted whenever the switching mechanism is adjusted. The casing 26 is provided at one end with an opening in which a conduit connection or a rubber grommet 3d may be inserted as shown. This serves for the purpose of providing an entry for the electrical connecting wires A cover plate for enclosing the casing 25 is provided which is held on the casing by means of a screw 37. The scr w 37 threads into a protecting plate 38 arranged immediately above the switching mechanism and which is secured to the sides of the casing by means of screws one of which is shown. A projecting edge of the plate 38 extends through an opening at in the side of the casing to further support the plate The plate 38 thereby serves to protect a portion of the mechanism and likewise serves as a securing means for the screw 3?. ()nc side wall of the casing 26 has a threaded projecting portion 4| formed integral therewith and into which the end of supporting tube i6 is threaded A lock nut i2 threaded on the tube 53 and tightened against the side wall of the casing 28 rigidly secures and locks the thermal device 5 and the switching mechanism 6 in associated operative relationship. This threaded engagement pro vi es a calibration or adjustment of the thermal device 5 within the casing l and of the switching mechanism to be pointed out. A compression spring 43 encircles the outside of the supporting tube id and exerts its force between the lock nut :52 and the rear of the s iielding disc la. The purpose of this spring 13 is to at all timeshold and maintain the disc 15 in its set position upon the shoulder formed in the cylinder i l of casing l. The disc 55 will remain on its seat and close 1e end of easing i regardless of the position to which the switching mechanism 8 may be longitudinally shifted when an adjustment of the position of the thermal device 5 is made.

Arranged in spaced relation to the bottom wall of the switch Casing is a fiat insulating plate i-'5, the general shape of which is shown in detail in 2. The plate 44 is supported by means of a number of bushings es riveted at one end to th bottom of casing 25 and screws threading into the bushings.

The switching mechanism 6 is of the so-called slip friction type, that is,'the contact is operated immediately upon initial mo of the mechanism and upon continued p sive movementa slipping action ta lies 'pla tween the elements while the, contacts remain closed. By this arrangement the contact mechanism is actuated immediately upon reversals of the switching mechanism caused by temperature changes. The slip friction mechanism comprises generally a lever means including a pair of identically shaped and oppositely disposed lever arms 41 and 48 which are pivoted together for movement about a pivot pin 49 which is supported on the insulating plate 44. A second pivot pin 50 connecting the lever arms 41 and 48 together passes through a movable element or link The link member 5| is adapted to freely rotate a limited amount about the pin 56 between the two lever arms and is provided with an axial bore into which the operating shaft l1 loosely projects. The lever arms 41 and 48 are connected together at one end by a pin 52 to which one end of a tension spring 53 is connected. The other end of spring 53 is connected to a supporting bracket 54 suitably secured to the bottom of casing 26 as shown. The foregoing arrangement of elements is such that the spring 53 normally exerts a pull upon the lower end of levers 41 and 48 as viewed in Fig. 2 and tends to urge the lever arms about pivot pin 49 so that the link 5| transmits this spring force longitudinally to the operating shaft I1. The shaft H as a result urges its shoulder against the rear side of diaphragm l6 thereby bulging it slightly outward at its center. From this arrangement it is seen that the diaphragm l8 upon being subjected to heat and as a result bowing outward permits the lever arms 41 and 48 to swing their upper ends in a clockwise direction as viewed in Fig. 2 and upon a drop in temperature affecting the diaphragm l8 the diaphragm forces the shaft IT in a left hand direction to rotate the lever arms 41 and 48 clockwise against the action of the spring 53. Since the spring 53 maintains the foregoing elements under a constant state of tension at the pivot points and link members, it is seen that the possibility of lost motion existing in the linkage is extremely remote. All moving parts therefor are actuated together simultaneously insuring the instantaneous reliable operation of the contact switching mechanism.

The slip friction mechanism proper includes a relatively thin steel blade 55 pivoted at one end to pin 49 and having a polished surface on both sides which is in intimate contact with separate graphite discs or blocks 56 and 56a arranged on each side of the blade 55 as seen in Fig. 3. Each graphite disc 56 and 56a is held in position on the blade 55 with tension by means of a thin spring blade 51 and 51a respectively which is supported at each end in oppositely disposed slotted openings in each lever 41 and 48. In order to adjust the degree of friction between the friction discs 56 and 56a and the blade 55, an adjusting screw 53 threads between the ends of the lever arms 41 and 48. By turning this screw the desired friction or compressive effort of the friction discs upon the blade 55 is obtained. The adjusting screw 58 is of sufficient length so as to serve as a stop for the lever arms by engaging the sides of a recess 59 formed in the insulating plate 44. The adjusting screw 58 also passes through one end of each spring blade 51 and 51a to hold it in position on the friction blocks 56 and 56a.

A switching arm 66 made of insulating material is secured to the friction plate 55 by means of rivets as shown. The switch arm 69 at its free end carries a bracket arranged to support a movable contact 62 supported upon a thin pressback spring blade 6|, as shown. The movable contact 62 is arranged in cooperative relationship with a fixed contact 63 which in turn is carried upon an angular metal bracket 64 attached to the insulating plate 44 by screws 65. The bracket 64 has a slotted opening in its turned up portion as seen in Fig. 4 through which a reduced portion 66 of the switch arm 66 projects. This slotted opening serves as a guide and slidable support for the end of the switch arm 60. An adjusting and stop screw 61 threaded through a projecting end of the bracket 64 is adapted to engage one edge of the switch arm 69 when the arm is in contact opening position. The adjusting screw 61 enables the switch arm to be adjusted to operate with any desired degree of movement. The bracket 64 is also provided with a terminal screw 68 to which one of the wires 35 is attached to establish a circuit path for the fixed contact 63. A second bracket 69 is supported as shown to the insulating plate 44 and carries a terminal screw 16 for attachment of the other connecting wire 35. The bracket 69 has a pig tail connection passing underneath the insulating plate 44 and connecting with the spring blade 6| of the movable contact 62. The irregular shaped bracket because of its particular construction serves for a multiplicity of purposes; it functions as a terminal screw support, a guide for the switch arm 69, a support for the fixed contact, and a support for the adjusting screw 6?.

Operation The combination control, including the thermal responsive device 5 and the switching mechanism 6, is arranged as a unitary structure supported as has been pointed out, upon the sides of a cylindrical blast tube ID of an oil burner installation 1| in the position indicated in Fig. 5. The unit is supported in such a manner that the opening l2 will be exposed and point into the combustion chamber of a furnace indicated generally at 12. The flame 13 produced by the operation of the burner 1! projects into the fire pot of the furnace in the general manner indicated and the opening I2 is so arranged that radiant heat emanating from the flame can pass through the opening l2 and impinge upon the front surface of the diaphragm IS. The diaphragm i8 is therefore so positioned in the assembly of the device as to be directly exposed to the temperature of the flame to which it is arranged to respond. Fig. 2 shows the switching mechanism including contacts 62 and 63 in their closed or cold position and if the fire is now started by the burner 1| in the well known manner, and combustion is produced in the furnace 12, the diaphragm,

l8 will rapidly become heated by radiant heat from the flame and tend to expand. Circumferential expansion of the diaphragm I8 is restricted because of its intimate association with the disc 2|! which does not heat up as fast as the diaphragm and which also expands a lesser amount than the diaphragm even when heated to the same temperature as the diaphragm. As a result the center portion or apex of the diaphragm l8 bulges outwardly. This action takes place almost immediately in response to combustion conditions in the furnace because the diaphragm is constructed of relatively thin material and absorbs the heat instantly. The outward movement of the apex of the diaphragm |8 permits the shaft H to follow this movement due to the follow-up movement of the levers 41 and 48 caused by the tension of the coil spring 53. The spring 53 at all times maintains a relatively close intimate relationship between the levers 47 and 48, the rod l1 and the diaphragm i 8 so that no lost motion can exist in the linkage. Upon the initial movement of the levers 41 and 38 about the pin 49 the friction blade 55 is caused to effect a movement also about pivot pin 49 by reason of the force exerted upon the blade by the friction discs 55 and 56a which carry the blade along when the levers are rotated The switch arm 86 is thereby swung in a clockwise direction as viewed in Fig. 2 so that the normally closed contacts 62 and 53 are immediately opened. The action of opening the contacts 62 and 63 produces a change in the circuit operating conditions of the oil burner l! in a manner well understood in the art for permitting the burner to continue to operate.

As the operating arm 63 rotates in a clockwise direction after opening the contacts 62 and 63 it encounters the adjustable stop screw 6?. When this point is reached further rotation of the switch arm 68 and the friction blade 55 is halted and the contacts remain in their open position. The diaphragm i8 however may continue to buckle outward as a consequence of greater elevated temperatures to which it may be subjected as the flame in the combustion chamber acquires greater intensity. As a result the spring 53 continues to exert a pivoting movement of the lever arms i? and 48 about pivot pin 49. The friction blocks 56 and 56a on each side of friction blade 55 can now frictionally slip across the surface of the blade 55 without causing further motion of the blade 55 and without straining any of the mechanism. Since the movement of all of the actuated elements is in a straight linear direction due to their arrangement substantially a unitary plane, there can be no stresses set up in any of the elements which may cause them to bend or flex in any manner. The diaphragm i3 is practically instantaneously responsive to radiant heat while the disc 2i! arranged on the rear of the diaphragm being of a greater mass responds somewhat at a slower rate and lags behind the response of the diaphragm.

When the burner 5! is shut down or in the event of combustion failure during a running period, the flame F3 in the combustion chamber ceases to exist. The drop in temperature is immediately manifested upon the diaphragm i8 which senses the reversal or change in temperature and because of its thinness begins to move immediately to a substantially flat position, as shown in Fig. 1. This movement of the diaphragm it is passed to the shaft i? by means of the washer engaging the rear of the diaphragm. The shaft I? causes levers 4'! and 48 to rotate against the tension of spring 53. The initial movement of levers di and 48 causes the friction blade 55 to move the switch arm 68 into contact closing position away from step screw 6?. Continued inward buckling of the diaphragm 18 causes the friction blocks $55 and 58a to slip on the blade 55 after contacts and 53 establish contact so that the mechanism can continue to move without straining the same.

In the event that the thermal responsive device 5 should develop a defect, burn off or become affected by any abnormal conditions the device is arranged to move into a fail safe position. That is. upon the automatic operation of the burner the device would operate under control of the tension spring 53 to cause opening of contacts 62 and 63 which would enable the burner H to start, but upon the automatic stoppage of the burner and the consequent extinguishment of the flame in the burner, the diaphragm or associated mechanism which is disabled, would fail to restore the contacts to their closed position with the result that a lock-out condition would occur in the burner circuit in the well known manner and prevent the further operation of the burner. The device therefore is arranged to provide for this fail safe feature in a simple and reliable manner.

It is contemplated in the present structure that the device may be utilized in a circuit arrangement in which the contacts 62 and 63 may be normally opened instead of closed as shown. This may be accomplished by simply reversing the position of the contacts and adjusting stop screw 61. Under certain conditions an arrangement of this type is desirable and to produce a fail safe condition with this arrangement, similar conditions would prevail as pointed out.

It is further contemplated that the unitary structure comprising the thennal responsive device 5 and the slip friction mechanism 6 be mounted in other positions than the top of the blast tube as illustrated in Fig. 5. For example it may be mounted on the side of the blast tube it! or any other position. Under these conditions and that in which it is shown in Fig. 5 the sloped portion #3 on the casing I is arranged to intercept the radiant heat which emanates from the edge of the flame within the burner. This portion of the flame does not produce a stable condition but wavers considerably and if it were permitted to transmit its heat rays to the diaphragm l3 erratic operation may result. Therefore the opening I2 of the casing 5 is so arranged as to point toward the most intense or most stable portion of the flame in the combustion chamber and permit only the rays from this portion of the flame to pass to the diaphragm i8.

In the modified form of the invention illus trated in Figs. 6 to 11 inclusive a casing or housing 83 similar to that shown in Fig. i is provided for housing the switching mechanism. In this form of the switching mechanism the elements comprising the same are constructed and arranged in a somewhat different manner from the elements of Fig. l, but they function and operate in a somewhat similar manner. Extending outwardly from the casing 86 is a small tube 8|, one end of which is connected as shown in Fig. 6 to the bottom of a cup-shaped member 62 arranged upon the wall of the casing 8! A plate member 83 encloses the end of the cup member 32. Both the cup member plate 83 are fastened to the side wall of the easing 85 by a plurality of screws 34. Arranged within the casing and having one end sealed against the outside wall of the cup member 82 is a condition responsive device shown in the form or" an expansible and contractible bellows 85. The other end of the bellows is connected with a link member The bellows communicates with the tube 8: and may contain a volatile gas or liquid having the properties of expanding when subjected to elevated temperatures. The bellows 85 when expanded moves the link member 35 in a left hand direction as viewed in Fig. 6 and is adapted to rotate a pair of bell crank lever arms 81 and 88 which are connected by a pin 89 to the bellows link 85. The bell crank arms 3? and 88 are pivoted for rotation about a pin 90 which is supported between a pair 82 and the of projecting bracket members BI and 92 formed in a supporting bracket member 93, the general shape of which is more clearly seen in Fig. 7. The supporting member 93 is supported in the casing 80 by screws 94 and 95 passing through opposite walls of the casing and into the supporting member 93.

A coil tension spring arranged within the casing 80 has one end connected to the free ends of both the bell crank arms 8'5 and 88 by means of a pin 91. The other end of the tension spring 96 is connected to a bracket 9% held onto the casing 89 by screw 8%. The spring 96 is arranged to exert its tension upon the free end of the bell crank arms and normally urge them about pivot 90 against the vapor tension of the bellows 85 so as to function as a restoring force for the bell crank arms when the bellows is contracted. The spring also functions to eliminate any lost motion at any of the pivot points.

A friction spring blade It!) in the form of a thin leaf spring having a polished surface loosely pivoted upon the pin an and arranged between the bell crank arms 81 and 88. Arranged for sliding frictional contact with the friction blade IE9 is a pair of friction elements or blocks Ill! and I02 arranged on opposite sides of the friction blade. The friction blocks It! and H32 are held in resilient intimate engagement with the friction blade Idil by means of leaf springs Hi3 and I04 engaging the friction blocks as shown in Fig. 8. One end of the leaf springs Hi3 and IN is rigidly secured to the respective bell crank arms 8'! and 38 while the opposite end extends through slotted openings inthe free end of the bell crank arms. In order to adjust the correct amount of tension and therefore the'frictional engagement of the friction blocks with the friction blade, an adjusting screw IE5 is threaded through the ends of the bell crank arms 8'1 and 8t and passes through the free end of the leaf springs I83 and Iiii to hold them in position. A switch arm I916 preferably made of insulating material is riveted as shown to the friction blade I530 and projects outwardly therefrom.

All of the foregoing elements are arranged within the casing 33 in a position below a flat insulating plate Iiil which is supported in spaced relation from the bottom of the casing by means of a pair of studs Iliil and screws I09 passing through the plate I81 and into the studs I08 at one side of the plate, while the opposite side is supported on top of the supporting member 93 by a pair of screws Il and I II as seen in Fig. 6. Supported on the bottom side of insulating plate I01 is a contact bracket Iii of irregular shape having a number of extensions formed thereon. This bracket H2 is supported by screws H3 and H4 from the plate It'l. A projecting portion of the bracket IIZ is provided with a slot through which an end I55 of switch arm IIlii projects. This slot serves for the purpose of guiding and slidably supporting this switch arm at its end. Another projecting portion of bracket I I2 carries afixed contact point H6. Fixed contact IIB engages a movable contact iIl' which is carried upon the free end of a press back spring H8 in turn supported from a bracket IE8 arranged on switch arm M35 as shown. The opposite end of bracket H9 is adapted to engage an adjustable stop screw I20 carried from a projecting portion of bracket H2. The screw I253 serves as a stop for the switch arm I08 when it moves from one position to another to open the contacts IIS and Ill.

Arranged upon the top side of insulating plate Ic'I is a pair of terminal plates HI and I22 which are supported on the plate I81 by means of screws I23 and I24 respectively. Wire attaching screws I25 and I25 carried by terminal plates I2I and I22 serve for the attachment of the connecting wires IZ'I which pass into the casing through a rubber grommet I28. An enclosing cover I29 for the mechanism within the casing 80 is held on the casing by means of removable screw I30 threading into the supporting member 93.

The means for operating the switching mechanism in this modified form of the invention differs from the thermal element 5 of Fig. l in that no positive mechanical connection between the combustion responsive device and the switching mechanism exists. The usual gun-type of burner IEI illustrated diagrammatically in Fig. 10 is shown arranged with its blast tube projecting through the body of the furnace 32 and the switching mechanism casing 88 is preferably mounted in close proximity to the burner I3l. The condition responsive element is here shown in the form of a ring shaped bulb I33 sealed at one end and connected at the other end with the tube 8i. lhe bulb I33 may be filled with a tam perature responsive gas or fluid. The bulb I33 is positioned and encircles the end of the blast tube l3I of the burner in a position within the furnace I 32. It is held on the blast tube by means of a metal strap IN, the ends of which are clamped together by a bolt I35. A number of clips I36 formed in the strap I34 support the bulb I33 in position within the furnace I32 so as to be subjected to the flame I31 when the burner is operating.

Operation In the operation of this modified form of the invention the contacts Hi3 and II! are normally in their closed position and upon establishment of combustion conditions by the burner I3I within the furnace I32 the heat from the flame I3! causes the vapor within the bulb I33 to expand. The expansion of the vapor manifests itself through the tube 8i within the bellows 85 causing an expansion of the same. With this arrangement the connecting tube BI may be of an indefinite length and therefore the casing 8E) containing the switching mechanism may be positioned at any desired remote point from the thermal element IE3 or at a location where the heat of the furnace would not have any effect upon the switching mechanism. The expansion of the bellows 85 causes the link member 86 to move in a-left hand direction'as viewed in Fig. 6, causing the bell crank arms 81 and 88 to rotate counterclockwise against the tension of spring 96 and about the pivot pin Q0. Upon the initial rotation of the bell crank arms the slip friction blocks fill and Hi2 exert sumcient frictional tension upon the friction blade Iliii to carry it along, thereby effecting a movement of the switch arm ltd and immediately opening the contacts I I6 and Ill. As the bellows 85 expands further the switch arm Hit eventually engages its bracket us with the adjustable stop screw I29. When this point is reached further motion of the switch arm I68 is halted. The friction blocks [0i and IE2 are thereby caused to slip along the friction blade not. The bellows thereby can continue to expand without building up stresses in any of the elements. The amount of frictional efiort of the friction blocks upon the friction blade is readily adjusted by means of the screw I05. It will be observed that the motion of the bell crank arms 8! and 83, the friction blade I00, and the switch arm I03 takes place in a linear direction and all elements are operated in the same common flat plane. This prevents any strain upon the mechanism and eliminates lost motion caused by pulling or bending of the elements. In addition, all of the elements are supported in a protected position below the insulating plate I01.

Upon the cessation of combustion conditions within the furnace the thermal element'I33 cools oiT resulting in the contraction of the bellows 85. The coil spring 96 immediately takes over the function of restoring the elements to their cold position. Upon the initial movement of the crank arms the friction blocks carry along the friction blade I it and move the switch arm I06 out of engagement with the stop screw I20.

Upon the closure of contacts IIS and II I. the

motion of switch arm I 06 and friction blade I 00 is halted and the friction blocks slip on the blade If!!! as the bellows 85 continues to collapse.

From the foregoing it is perceived that the improved slip friction mechanism in combination with the associated thermal responsive means is of simple construction, reliable in operation and is arranged to safeguard the operation of a burner in a reliable manner. By combining the switching mechanism 6 with a thermal element into a single unitary structure as illustrated in Figs. 1 to 5, or remotely associating the switching mechanism 6 with the thermal element as illustrated in the modified form of the invention, a reduction in the wiring and installation cost is effected as well as a simplification of the testing, assembling, and matching of the units.

While a preferred form of the invention is illustrated as well as a modified form, it is contemplated that various modifications of the same may be made without departing from the general spirit of the invention, and it is therefore to be understood that the invention is not limited to the precise construction illustrated and described but only by the scope of the appended claims.

What is claimed is:

1. In a switching mechanism, in combination, a condition responsive element, a supporting base, a lever arm on said base actuated to one position by said condition responsive element, spring means on said base for restoring said lever arm after having been actuated, a friction blade pivoted to said base independently of said lever arm and having a limited movement on said base, slip friction means connecting said friction blade and said lever arm, and control means on the base operated by the movement of said friction blade.

2. In a switching mechanism, in combination, a condition responsive element, a supporting base, a lever arm and a friction blade independenly pivoted upon said base, slip friction means connecting said friction blade and said lever arm, means connecting said condition responsive element with said lever arm for causing said friction blade to be operated to one position through said slip friction means when the condition responsive element moves in one direction, means on said base connected to said lever arm for causing said friction blade to be operated to another position through said slip friction means when the condition responsive element moves in another direction, and control means operated difierently by said friction blade in each of its positions.

3. In a flame detecting control mechanism, the combination of, a plate-like member adapted to receive radiant heat from the flame, confining means associated with opposite edges of said member for causing said member to buckle when heated, a lever, direct connecting means between said lever and member, a spring for biasing said lever and member in one direction, said spring determining the direction in which the member buckles when heated and taking up lost motion between the parts, a friction blade, slip friction means connecting said friction blade with said lever, and control mechanism actuated by said friction blade.

4. In a control mechanism, in combination, a condition responsive element, a lever arm connected thereto, a pivot about which said lever arm is rotated by said condition responsive element, a friction blade independently rotatable about said pivot, a control arm carried by said friction blade, stops for said control arm, slip friction means arranged between said friction blade and said lever arm whereby said control arm is operated by the movement of said lever arm until the stops are encountered, said lever arm, said friction blade and said control arm all arranged in a common plane for pivotal movement about said pivot.

5. In a control mechanism, in combination, a condition responsive element, a lever arm connected thereto and operable thereby, a friction blade, a control arm carried by said friction blade, slip friction means arranged between said friction blade and said lever arm, and a common pivot point for said lever arm and said friction blade about which said slip friction is operated and said control arm is actuated, said lever arm said friction blade and said control arm all arranged in a common operating plane, and control means operated by said control arm.

6. In a control mechanism, in combination, a condition responsive means, a lever arm operable thereby, pivot means arranged between the ends of said lever arm and about which said lever arm is rotated, biasing means on one end of said lever arm for restoring the lever arm after having been operated by said condition responsive means, a slip friction means arranged at the other end of said lever arm, a friction blade cooperating with said slip friction means and independently rotatable about said pivot means, a control arm connected to said friction blade and operated thereby, and control means actuated by the operation of said control arm, said lever arm said friction blade and said control arm all arranged in a common operating plane rotatable about said pivot means.

7. In a slip friction control mechanism, a lever arm, means for pivoting said lever arm for rotation, a friction blade pivoted to said pivoting means for independent rotation thereabout, slip friction means arranged on said lever arm, resil ient means on said lever arm for resiliently engaging said slip friction means with said friction blade, means on said lever arm for adjusting the degree of frictional engagement of the slip friction means with the friction blade, stops for limiting the rotation of said friction blade, and control means actuated by said friction blade.

8. In a slip friction control mechanism, a lever means comprising a pair of oppositely disposed lever arms, pivot means arranged between the ends of said arms and about which said lever arms are rotated, a friction blade pivoted to said pivot means and having a portion arranged between said lever arms, slip friction means arranged upon each of said lever arms and engaging said friction blade, means on each arm engaging said slip friction means for resiliently holding said slip friction means against the friction blade, adjusting means between said lever arms for adjusting the degree of friction with which said slip friction means engages said friction blade, and a control device actuated by said friction blade.

9. In a slip friction control mechanism comprising, in combination, a condition responsive element, a linearly movable shaft actuated thereby, a base, a lever arm pivoted to said base and rotated by said movable shaft, a friction blade pivoted to said base, said lever arm comprising two portions thereof between which said friction blade is arranged, friction means on said lever arm engaging opposite sides of said friction blade, means on said lever arm for resiliently holding said friction means in engagement with said friction blade, stops on the base for limiting the rotation of said friction blade, said lever arm arranged to slip said friction means across the surface of said friction blade after the friction blade encountersone of said stops, and a control arm connected to said friction blade and operated by the movement thereof, said lever arm, said friction blade, said control arm, said movable haft and said slip friction means all arranged to operate in a single common plane upon said base.

10. In a control mechanism, in combination, a condition responsive element, a rotatable lever arm, a pivot pin on said lever arm to which said condition responsive element) is connected, a supporting base, a pivot pin for said lever arm mounted on said supporting base and about which said lever arm is rotated by said condition responsive element, a friction. blade pivoted to said last mentioned pivot pin, slip friction means i arranged upon one end of said lever arm and engaging said friction blade for operating the same, a spring connected to the opposite end of said lever arm for rotating said lever arm back to its initial position after having been operated by said condition responsive means actuated by the movement of said friction blade.

11. In a control mechanism, in combination, a condition responsive element, a rotatable lever arm, a pivot pin arranged between the ends of said lever arm and to which said condition responsive element is connected, 2, second pivot pin arranged between the endsof said lever arm for supporting said lever arm upon the base for movement by said condition responsive element, a spring connected to said lever arm at a point remote from said second pivot pin, slip friction element, and control means carried by said lever arm at a point remote from said second pivot pin, a friction blade having one portion engaged by said slip friction means and another portion connected to said second pivot pin for rotation thereabout, and a control arm supported by said friction blade and operable thereby.

12. In a switching mechanism, a supporting plate, a switch arm pivoted for movement on said upporting plate, an angular shaped bracket supported upon said plate and having a plurality of projections formed thereon, means on a first one of said projections for supporting and guiding the free end of said switch arm, means on a second one of said projections for adjustably limiting the movement of said switch arm, contact means on a third one of said projections actuated by said switch arm, and wire terminal connecting means for said contact on a fourth one of said projections.

13. In a control mechanism, in combination, a lever, a fixed pivot for said lever, condition responsive means for rocking the lever about said pivot upon change in the condition to which the condition responsive means responds, a friction blade independently pivoted upon said pivot adjacent aid lever, control means operated by said friction blade between predetermined limits of movement, and slip friction means carried by said lever and engaging said friction blade, said slip friction means tending to cause rocking of the friction blade about said pivot upon rocking of the lever about said pivot.

14. In a flame detecting switching mechanism, the combination of, a plate-like member adapted to receive radiant heat from the flame, confining means associated with opposite edges of said member for causing the member to buckle when heated, a movable member, connecting means between said movable member and said plate-like member for transmitting all buckling or unbuckling movement of said plate-like member to said movable member whereby the movable member assumes various positions corresponding to various positions of said plate-like member, said connecting means including a spring for positively biasing said movable member and plate-like member in one direction to determine the direction in which the plate-like member buckles when heated and for taking up lost motion between the parts, a second movable member, control mechanism operated by said second movable member, and slip friction means interposed between said first and second movable members, said slip friction means being separate from and independent of said spring whereby the tension of said spring does not affect the action of said slip friction means.

HOMER E. MALONE. 

